Influence of polarity of medium on formation of intermediates in photolysis of alkylaminobenzophenones in solutions

Flash photolysis has been used in a study of the absorption spectra and decay kinetics of the intermediates in photolysis of 4,4′-bis-dimethylaminobenzophenone, 4,4′-bis-diethylaminobenzophenone, and 4-dimethylamino-benzophenone in various types of solvents. It has been established that flash photolysis of solutions of alkylaminobenzophenones in polar solvents produces not only alkylamine or ketyl radicals, but also an intermediate that absorbs in the 470 nm region, the decay curves of which are described by first-order kinetic equations. In the presence of tertiary amines, the yield of this product is lower. The addition of sodium perchlorate to the solution increases the lifetime of this intermediate species. L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of the Ukraine, 31 Nauka Prospect, 252039 Kiev, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 1, pp. 27–31, January–February, 1997.     

Influence of the polarity of the medium on the rate of oxidation of unsaturated compounds

Russian Chemical Bulletin -     

Influence of medium polarity on the photosensitizing properties of hematoporphyrin and hematoporphyrin derivative (Photofrin II)

The influence of the polarity of the medium on the efficiency of Type I and Type II photosensitization as carried out by hematoporphyrin and its derivative Photofrin II was studied by EPR techniques. Our results suggest that porphyrin aggregates do not participate as such in the photosensitized processes. Thus, the solvent-induced breakdown of the aggregated components of Photofrin II appears to determine the photosensitizing efficiency of this porphyrin.     

A spectroscopic study on medium polarity in fluorous alcohol

The paper describes the polarities of three fluorous (F) aliphatic alcohols: perfluorinated tert-butanol (F-t-BuOH), n-butanol (F-n-BuOH), and n-heptanol (F-n-HepOH). For the purpose, we conducted absorption and fluorescence spectroscopies of coumarin 153 (C153) and 102 (C102) in three F and 13 non-fluorous (non-F) alcohols and determined their maximum energies: ν^a (absorption) and ν^f (fluorescence). We obtained linear relationships between the Stokes shifts of the dyes (i.e., (ν^a − ν^f)) and a medium polarity parameter for 13 non-F alcohols, f(x): f(x) = [(D_s − 1)/(2D_s + 1) − (n² − 1)/(2n² + 1)], where D_s and n were the dielectric constant and refractive index of a solvent, respectively. By comparing the Stokes shifts of the dyes in three F alcohols with those in 13 non-F alcohols (i.e., (ν^a − ν^f) vs. f(x) plot), the D_s values in F-t-BuOH, F-n-BuOH, and F-n-HepOH were evaluated to be 2.7-3.9, 4.3-5.1, and 4.0-5.2, respectively, while those in the relevant non-F alcohols were 12.5, 17.5, and 12.9, respectively. Thus, the present experiments demonstrated that the polarities of these F alcohols were much lower than those of the relevant non-F alcohols.     

Influence of culture medium characteristics on the ability to oxidize low-density lipoproteins

Five culture media, differing in terms of their metal ion (Fe and/or Cu) and antioxidant contents, and used for endothelial cell-low-density lipoprotein (LDL) interaction studies, were characterized electrochemically. Measurement of the redox potential of the solutions and plots of the cyclic voltammograms revealed marked differences in potential and the rate of oxygen reduction. However, there were only very weak correlations between these electrochemical properties and the capacity of the media to oxidize LDL in the absence and presence of endothelial cells. In contrast, this capacity was strongly correlated with the presence of metal ions, which may act via conformation changes of LDL.     

Effect of polarity of medium on thermal stability of 1,4-benzoquinone diazides

Conclusions The thermolysis rate of 1,4-benzoquinone diazides in aprotic media is independent of the polarity of the solvent, as well as of the electronic and steric effects of the substituents in the quinone diazide nucleus; in protic media, due to complexing with the solvent, the thermolysis rate of the quinone diazides is determined by the steric effects of the substituents and the polarity of the medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2628–2631, November, 1981.     

The influence of solvent polarity and viscosity on fluorescence of quinolizinium salts

The effects of dielectric constant, viscosity and polarity of the solvents used on the relative fluorescent emission of 2,3-diphenylquinolizinium bromide and 2(p-dimethyl-amino)styryl-3-methylquinolizinium bromide are described. These salts were entirely dissolved in ten different solvents. The 2(p-dimethylamino)styryl derivative produced different ionic species, and was a fluorescent acid-base indicator. The fluorescence of these quinolizinium salts is shown to increase with greater viscosity of the medium.     

Influence of medium polarity upon selectivity and efficiency of alkali metal cation sorption by polyether carboxylic acid resins

The influence of medium polarity upon competitive sorption of alkali-metal cations from aqueous and aqueous methanolic solutions by the polymethacrylic acid resin Amberlite CG-50, two acyclic polyether carboxylic acid resins, and six sym-(alkyl)dibenzo-16-crown-5-oxyacetic acid resins has been investigated. Addition of methanol was found to strongly depress the selective Li(+) sorption of CG-50 and one of the acyclic polyether carboxylic acid resins. Enhancement of metal ion-crown ether interactions as the percentage of methanol in the medium was increased accentuates the Na(+) sorption selectivity for the lariat ether carboxylic acid resins. The highest Na(+) sorption selectivity was obtained for sym-(alkyl)-dibenzo-16-crown-5-oxyacetic acid resins with ethyl and propyl groups in 80% methanol-20% water.     

Influence of the polarity of the medium on the oxidation of 2,4,6-triphenylverdazyl by compounds with a “positive” halogen

The kinetics of the reaction of 2,4,6-triphenylverdazyl with 2-bromocyclohexylbromoalonodinitrile was studied at 25°C in a benzene-nitrobenzene mixture and in pure solvents (C₆H₆, C₆H₅Cl, CCl₄) in the range 2<7. The Kirkwood equation (_ne=12.88D) was used to estimate the polarity of the transition state, and the Amis equation (r_ne=6.42 Å) to estimate the effect of radius of the activated complex. In a complex the proportion of transferable electronic charge is equal to 0.42, which permitted the reaction under study to be assigned to the S_N2 type.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 613–615, September–October, 1985.     

Drastic changes in the fluorescence properties of NBD probes with the polarity of the medium: involvement of a TICT state?

The spectroscopic and photophysical properties of two 7-nitrobenz-2-oxa-1,3-diazol-4-yl (NBD) derivatives with different substituents on the nitrogen group are reported in 18 solvents. The solvatochromic shifts were analysed by correlating with polarity scales. The results, together with the help of modified neglect of diatomic overlap (MNDO) calculations, enable the polarity of the ground and first singlet excited states to be determined. Experiments based on variations in temperature and viscosity establish that the two probes undergo different de-excitation pathways. The possibilities of internal rotation leading to a twisted intramolecular charge transfer (TICT) state in the case of diethylamino-NBD are discussed. A study in binary solvent mixtures outlines specific solvent—solute interactions. Appropriate restrictions are emphasized on the utilization of NBD probes in biological fields.     

Modulation of diarylethene fluorescence by photochromic switching and solvent polarity

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A tetraphenylethene based polarity dependent turn-on fluorescence strategy for selective and sensitive detection of Hg in aqueous medium and in living cells

A turn-on fluorescent chemosensor strategy based on the change in the polarity of aggregation induced emission active tetraphenylethene is presented for the detection of Hg²⁺ in aqueous medium and in living cells. The sensing mechanism involves the formation of nonpolar fluorescent aggregates of tetraphenylethene molecules by elimination of polar moieties of TPE with Hg²⁺ interaction.     

A polarity dependent fluorescence "switch" in live cells

The spectroscopic properties, ultrafast kinetics and utilization of a photochromic molecule as a bi-stable fluorescing sensor of polarity in live cells are described. This molecule is a photochromic fulgimide, 2,3-dialkylidenesuccinimide, which emits fluorescence that can be switched optically on and off. The fluorescence intensity is a function of the polarity of the molecular environment, namely it fluoresces strongly when the molecule is in its polar isomeric structure form. We demonstrate that this molecule enters live cells without inducing damage, it binds primarily to internal membranous organelles (mitochondria) and its fluorescence can be switched optically "on" and "off" repeatedly while inside the living cell. A possible use as a bi-stable, on/off sensor is discussed.     

A cold silanization method for preparation of medium polarity capillary columns

Silane-coupling agents, commonly used for fiberglass reinforced plastics (FRP), were applied for deactivation of silanol sites in glass capillary columns prior to coating with mediumpolarity phases such as Carbowax and Superox. The columns, prepared in a two-stage process in the case of glass (acidic leaching and drying, dynamic cold silanization followed by static coating with the phase) or a one stage process in the case of fused silica, gave the best results when deactivation and hence wettability were induced by glycidoxypropyltrimethoxy silane.     

Study on fluorescence characteristics of duloxetine hydrochloride

The fluorescence characteristics of duloxetine hydrochloride are studied in this paper. The fluorescence emission spectra of duloxetine demonstrate that intramolecular charge-transfer takes place between thiophene ring and napthalenyloxy group upon irradiation. The effects of excitation light, solvent system, variation of solution pH value, metal ions and vitamin C on the fluorescence spectra of duloxetine hydrochloride are elucidated, respectively. A spectrofluorometric method of quantitative determination of duloxetine in dosage form is reported for the first time, the linear range is 7.14 x 10(-8)mol/L to 1.43 x 10(-5)mol/L, the linear correlation coefficient r is equal to 0.9997, and the detection limit is 3.5 x 10(-8)mol/L. The accuracy and the precision are satisfactory.     

Influence of solvent polarity and medium acidity on the UV-Vis spectral behavior of 1-methyl-4-[4-amino-styryl] pyridinum iodide

Electronic absorption, and excitation spectra of 1-methyl-4-[4-aminostyryl] pyridinum iodide (M-NH2) were measured in solvents of different polarity. The (M-NH2) dye exhibits negative solvatochromism, i.e. a hypsochromic band shift as the solvent polarity increases. The fluorescence quantum yield is also sensitive to the polarity and viscosity of the medium. The ground and excited state protonation constants were calculated and amount to 3.35 and 0.62, respectively. The effect of micellization on the emission spectrum of (M-NH2) are also studied in sodium dodecyl sulphate (SDS). The fluorescence intensity increases as the concentration of SDS increases with an abrupt change at cmc. The quantum yield of the cis trans photoisomerization is also determined in aqueous buffer solution of pH 1.1.     

Effect of polarity of the medium on the stereospecific polymerization of propylene by ansa-zirconocene catalyst

Propylene was polymerized with rac-ethylene-bis (1-η⁵-indenyl)dichlorozirconium/methylaluminoxane in solvents of different polarity. The poly (propylene) formed was separated by solvent extraction; ¹³C-NMR and DSC measurements were made on the polymer fractions. The poly(propylene) in each solvent fraction has its characteristic molecular weight steric pentad distributions, melting transition temperature, and enthalpy for fusion irrespective of the polymerization medium. The results suggest that the medium dielectric constant does not affect the polymerization rate or the intrinsic stereoselectivity, propagation and chain transfer rates a given catalytic species but can alter the occurrence of steric insertion errors through shifting of distributions of the propagating species producing poly(propylenes) of different stereoregularities. © 1994 John Wiley & Sons, Inc.     

Separation of oligomers of medium polarity by packed column supercritical fluid chromatography

Chromatographia - Several different oligomers containing polar groups either in the backbone or in the side chains were successfully separated by SFC on polystyrene stationary phases. Composition...